- A Lewis acids are molecules/ions that can accept a pair of nonbonding
electrons to form a covalent bond. Not surprisingly, molecules/ions that
contain an atom with an incomplete octet are good Lewis acids. The only
choice that has an atom without a stable octet (or bitet in the case of H) is
the carbon in choice (A).
- D According to the reaction, 6 Ca atoms are present in the reactants.
Therefore, 6 CaSiO 3 must be present as products, choice (D).
- B Percent by mass is calculated by dividing the mass of the solute by the
total mass of the solution. 40.0 mL of water would have a mass of 40.0 g
(density of water = 1.0 g/mL), so the total mass of the solution would be
10.0 g + 40.0 g = 50.0 g. Then, (10.0 g/50.0 g) × 100% = 20%
- E Given that the molecular weight of AgCl is 143.4 g/mol, the number of
moles of AgCl precipitated is
Moles AgCl = 5.70 g/143.4 g/mol
= 0.040 moles
Since the molar ratio of Ag+ in AgCl is 1, the number of
moles of Ag+ in the original solution was also 0.040.
Therefore, the concentration of the original solution was
Molarity Ag+ = moles Ag+/volume (L)
= 0.040 moles/0.100 L
= 0.40 M (choice E)
- A Choices (B), (C), (D), and (E) are all true statements. Choice (A) is a
false statement—the vapor pressure of a substance depends only upon 1)
the substance’s temperature and 2) its mole fraction when it’s in solution
(see the colligative property of vapor pressure depression).
- B This is a bit of a trick question; when using any gas law that involves
temperature the Kelvin scale must be used. However, Boyle’s Law (P 2 V 2
= P 2 V 2 ) is only used when temperature is held constant, and thus, the
